These numbers seem straightforward and easy to understand. Furthermore, the MMR vaccine is widely available, and its use is covered as a preventive service by insurance plans.

Despite these facts, our vaccination rates are less than ideal. In fact, a recent study in JAMA Pediatrics(archpedi.jamanetwork.com) suggests that the vaccination rate among people exposed to measles during the recent Disneyland outbreak was less than 86 percent at best and may have been as low as 50 percent. To establish herd immunity against the measles, a population's vaccination rate must be at least 96 percent. Thus, the outbreak spread to 145 people in seven states, as well as to others in Canada and Mexico.

Nationally, nearly 95 percent of kindergarten students(www.cdc.gov) had received two doses of MMR during the 2013-14 school year, but rates varied widely by state. Eight states had coverage rates below 90 percent, including Colorado's dangerously low 81.7 percent.

So how did we get to this point, and how do we turn it around? It has been more than five years since The Lancet retracted the flawed study that linked the MMR vaccine to autism. Yet we continue to battle the anti-vaccine sentiment that study fueled.

Earlier this year, the Pew Research Center released a report(www.pewinternet.org) that examined how the general public perceives scientific matters compared to the views of scientists. On the matter of vaccines, 86 percent of scientists surveyed (up from 82 percent in 2009) said vaccines such as MMR should be required for children. Conversely, only 68 percent of the public agreed that vaccines should be required.

The numbers were even more striking when broken down by age. Nearly 40 percent of people under age 50 said parents should be able to decide whether or not to vaccinate their children, compared to 22 percent of people 50 and older.

Rather than asking parents about vaccines, physicians should simply be telling parents that their children are due for medically recommended vaccines. A 2013 study in Pediatrics(pediatrics.aappublications.org)revealed that when physicians allowed discussion about whether or not to vaccinate, less than 20 percent of parents opted to vaccinate their children. Conversely, when physicians presumed parents would vaccinate their children, more than 70 percent of parents had their children vaccinated.

Finally, the CDC, in collaboration with the AAFP and the American Academy of Pediatrics, offers free resources(www.cdc.gov) to help physicians talk to parents about vaccinations. The tools include immunization schedules and information about vaccine-preventable diseases, as well as information for parents who choose to delay or decline immunizations.

The Disneyland outbreak was possible because vaccination rates in many of our communities are unacceptably low. Until that changes, the threat of new outbreaks remains a stark reality.

Paul Hunter, M.D., a former AAFP Vaccine Science Fellow, is an assistant professor in the Department of Family Medicine at the University of Wisconsin School of Medicine and Public Health and associate medical director for the City of Milwaukee Health Department.